1. Field of the invention The present invention is directed to an electronic detector for locating an object behind a wall surface, and more particularly, to such a detector capable of distinguishing between a metallic object and non-metallic object concealed behind a wall surface.
2. Description of the prior art There is already known an electronic wall stud detector which is utilized to move along a wall surface to detect a wall stud or the like behind the wall surface, as proposed in U.S. Pat. No. 4,099,118. The patent disclose the sensor which detects the presence of the stud behind the wall surface by measuring a change in the capacitance of the wall due to the presence of the stud. Although the detector is found useful in many sites, it is not satisfactory in a particular site where it is required to distinguish between a non-metallic object and a metallic object such as metal pipes for water and electric cables routed within the wall, since such metallic object should be kept harmless when a nail or the like member is driven into the wall. It is therefore most desirable to distinguish the metallic object and the non metallic object both positioned within the wall.